*Knuckle crack time.* All right, lets do this.
Underwater photography is, in simplest terms, a **** of a thing to get right. For quite a few reasons.
Firstly, however, lets break down the possibilities, and then I'm going to ask you some questions.
You can either buy a housing for your current camera. This is, in point of fact, actually one of the more expensive ways to go. Depending on the camera you have, the housing can actually be pretty damn expensive, and I'd recommend getting a reputable one or one with a lot of believable recommendations. If it is not, you could get a case that is either slightly wrong or not as waterproof as the package says. Either way it is a disaster. Each case is a custom fit for each camera, as the dials, buttons and the like are, pretty much without fail, in different places on every single camera. So you have to get the specific one.
The second option is getting a camera that is already waterproof. Spend around $400 (at most) and you should get a camera with a decent depth (say ten meters). There are, however, going to be problems, that few people touch on. And they all have to do with the complex parts of photography.
The problem comes down to light. The deeper into water you go, the less light you get. The less light you get, the more the camera needs to push up its ISO to compensate. The more it has to push it up to compensate, the more grain you get in the photo. Either that or blurry images. Flash won't carry as far underwater either, unless its a very powerful one.
At ten meters down, for example, the amount of usable light is significantly reduced. Even direct sunlight above you will get lessened considerably. It will slow down your shutter speed as a result, and you are going to be more prone to getting poorly focused or flat out blurry shots, or taking far too long to focus the shot, losing the shot you want.
How you get around this is not exactly simple.
First, for the optimum result, you want what I call a direct pass lens - in other words, a lens system that is set with the sensor directly behind it. Most waterproof cameras have the lens set in a corner. This creates two problems. First, it is INCREDIBLY easy to get a finger in the photo, and two, the setup of the lens array involves mirror bouncing. It has a habit of losing light along the way, meaning you are already on a backwards footing. You want to get the ISO down on a compact camera as much as you possibly can at all times - they very rarely do a good job at higher ratings, unless its one of the better brands. For example, Panasonic and Olympus do underwater compacts, and have for some time, but they are truly awful when it comes to their noise reducing algorithms compared to, say, Canon. Canon has in fact, I believe, come up with an underwater camera. It doesn't have a direct pass lens, however, and I've not gotten to use it yet, so it might be a bit sub par. The other one is one by Olympus (also one I've not yet seen) which, despite being a poorer ISO performer, does have a direct pass lens and a very, very low minimum aperture of just f/2.0.
I should probably mention that. You want a lens with the best, lowest aperture possible. It means you get less in focus at a time, but it also means more light passing through the lens (aperture being the thing that controls depth of field and amount of light hitting the sensor, affecting shutter speed to match the amount of light).
You can get some good results if you look around. Gopro is a good one, but can be expensive for the best results, and they tend to mostly do movie. They are tough as nails however.
The best result would be an SLR, of course, with a proper diving rig. But getting all that will probably mean delaying the trip for a couple of years to pay for it all. They get fearfully expensive for the good stuff.
But asking some questions first -
What do you have?
What are you prepared to spend?
How good a result do you want? (Photo album, basic snaps, framed picture, professional).